1. Field of the Invention
This invention relates in general to the construction of vaporizers and in particular to a new and useful anesthetic vaporizer which includes a bypass line connecting the gas inlet with the gas outlet and a guide for the flow of the portion of the gas to be vaporized through the vaporizing chamber and for subsequently combining it with the bypass gas.
2. Description of the Prior Art
In anesthetic vaporizers, a gas current passing through the vaporizing chamber over a reservoir of the anesthetic is enriched with the anesthetic to a desired concentration. In the known bypass anesthetic vaporizers, the desired dosing is obtained by dividing a total current into a bypass current, comprising a part of the total gas current in an unchanged gas composition, and into the vaporizing chamber current. The vaporizing chamber current comprises the balance of the total gas flow and this is enriched in the vaporizing chamber with the anesthetic in order to saturate it. This is generally achieved by passing vaporizing chamber current over a wick which dips into the liquid and which is saturated by capillary action with the liquid anesthetic. The gas is passed over the wick for as long as necessary to saturate the gas in accordance with its vapor pressure at the respective temperature. In order to insure saturation of the vaporizer chamber current with the anesthetic under all circumstances, that is also at maximum flow, a relatively large evaporation surface and thus a large vaporizer chamber volume are required.
But a large vaporizer chamber volume cannot counteract the necessary constancy of the anesthetic concentration at a pressure variation which occurs during respiration or use of the gas in breathing. This is because the vaporizer chamber current can get into the bypass line in an expansion of the respiratory gas from the vaporizer chamber backwardly. In this way inadmissibly high concentrations can be formed at the outlet of the anesthetic vaporizer.
A known bypass anesthetic vaporizer has two wicks designed as cylinders and they differ slightly in their diameter so that an annular interval, corresponding to the diameter difference, is formed between them, and which are assembled at the same level. The larger wick cylinder is arranged on the inside of the cylindrical chamber wall forming the vaporizer chamber. The smaller wick cylinder bears on the outside diameter of a cavity reducer arranged in the cavity of the vaporizer chamber. The bottom ends of the two wick cylinders protrude into a liquid anesthetic. The vaporizer chamber current enters into the vaporizer chamber from the top, flows over the surface of the anesthetic and is enriched slightly with the anesthetic and issues again through an annular interval between the two wick cylinders, which are wetted with the anesthetic by capillary action, and flows upwardly from the vaporizing chamber and combines with the bypass current.
The generatrix of the wick cylinders is very small compared to the space required for their combination. The flow conditions and thus the evaporation of the anesthetic can be insured optimally in the narrow and not exactly defined annular interval between the wick cylinders. In order to insure the necessary saturation of the vaporizer chamber current under all circumstances, the wick cylinders, and thus also the space which determines the dimensions of the anesthetic vaporizers, are made very large. The large cavity formed by this design of the wicks must be reduced by a cavity reducer and this only increases the weight of the vaporizer in order to prevent the dreaded return of the vaporizer chamber current at pressure variations during the respiration.
Another known anesthetic vaporizer according to the bypass system has similar wick cylinders but they are separated by a circumferential gas carrying spiral. This insures a uniform spacing distance. Besides, the spiral forces the anesthetic to flow over a certain path past the wick surfaces saturated with the anesthetic. The return of the vaporizer chamber current at pressure variations caused by the respiration is to be prevented by a pressure compensation spiral. This is arranged above the wick cylinders. The vaporizer chamber current flows in the order pressure compensation spiral, the spiral interval and the anesthetic surface, and combines again with the bypass current. Even an anesthetic vaporizer of this type is still very large. This, in addition to the space requirement, impairs its handiness.